1. Field of the Invention
The present invention relates to a manufacturing method for a semiconductor substrate and a manufacturing method for a semiconductor device, in particular, to a manufacturing method for a high quality, high performance semiconductor substrate wherein strain is introduced due to the provision of a SiGe film and to a manufacturing method for a semiconductor device utilizing same.
Presently, reduction in the amount of power consumed by semiconductor devices, in particular by CMOS devices, is necessary for saving of natural resources. Until the present, the lowering of the operating voltage of MOS transistors has been achieved by securing the driving performance through miniaturization of the gate structure and through reduction in the thickness of the gate film.
Miniaturization of the transistor structure, however, requires great technological innovation for each generation and a further increase in the burden on developers, and increases in investment cost.
Therefore, the following techniques have been proposed as techniques for securing the driving performance of a MOS-type field-effect transistor at a low power supply voltage without regard to further miniaturization of the transistor: (1) a method for securing the driving performance of a transistor by adopting a complete depletion-type SOL transistor structure in order to reduce the S value (inclination of current relative to voltage in the sub-threshold region) and (2) a technique for increasing the driving performance of a transistor through the adoption of a strained silicon channel structure utilizing germanium.
However, an SOI-type transistor device according to technique (1) described above requires a complete depletion-type SOI structure. Therefore, the formation of transistors in a thin film 501 layer having a thickness of approximately 50 nm, or less, becomes necessary wherein a process technology is required that has a precision higher than that of the transistor process using a bulk substrate. In addition, an SOI layer is surrounded by a buried oxide film, from below, and by an element isolation oxide film, from the sides. Therefore, a problem arises that the design means utilized for a device in a bulk substrate cannot be utilized without change.
On the other hand, a transistor channel can be formed using a silicon layer having tensile strain and formed on a layer of eutectic crystal silicon (hereinafter specifically referred to as “SiGe”) containing germanium of a differing lattice constant of which the strain has been relaxed. The driving performance of the transistor having a strained silicon channel structure according to technique (2) as above described is increased. That is to say, as is known from references (IEDM Tech. Digest, 1994, pp. 373–376, and the like), the effective mass of an electron is reduced in silicon having tensile strain in comparison with in unstrained silicon and mobility is increased and, therefore, the driving performance of a transistor can be increased through the utilization of this characteristic.
Many prior art references propose the application of the above described strained silicon in an NMOS transistor. In Japanese unexamined patent publication No. HEI9 (1997)-82944, for example, a buffer layer 52 having a concentration gradient is formed on a silicon substrate 51 so that lattice strain, caused by lattice mismatch between silicon film and SiGe film, is relaxed. A silicon layer 53 having a low lattice constant is deposited on top of the buffer layer in order to be utilized as a strained silicon channel, as shown in FIG. 3. Buffer layer 52 having a concentration gradient of germanium is utilized in this MOS transistor in order to suppress the occurrence of dislocations at the interface between the silicon substrate and the SiGe film so as to relax the stress due to lattice mismatch in the SiGe film. Accordingly, it is necessary to form a gentle concentration gradient in this MOS transistor and, consequently, a thick film buffer layer, on the order of μms, is required.
The deposition rate, however, of a SiGe film that utilizes epitaxial growth is usually as low as from approximately several nm per minute to several tens of nm per minute in order to secure monocrystallinity. Therefore, a long period of time is required for the deposition process, which can be problematic in terms of processing efficiency.
In addition, a technology utilizing ion implantation in order to control stress in a SiGe film is described in, for example, Japanese unexamined patent publication No. 2001-110725.
According to this method a SiGe film 62 is formed on a silicon substrate 61, as shown in FIGS. 4(a) and 4(b), and a first ion implantation of oxygen, nitrogen, or the like, into the interface between silicon substrate 61 and SiGe film 62 is carried out so as to form a stopper layer 64 for prevention of solid phase growth, as shown in FIG. 4(c). After that a second ion implantation of Ge, Si, or the like, is carried out so as to convert the lower portion of SiGe film 62, having a predetermined thickness, into an amorphous state, as shown in FIG. 4(d), and an amorphous layer 65a is converted by means of annealing into a monocrystal layer 66 wherein crystal defects have been reduced, as shown in FIG. 4(e). Then, as shown in FIG. 4(f), a third ion implantation of Ge, Si, or the like, is carried out so as to convert the upper layer portion of SiGe film 63 into an amorphous state and an amorphous layer 65b is converted into a monocrystal layer 66 by means of reannealing.
That is to say, implantations of ions having comparatively large masses and annealing are repeated a plurality of times on a SiGe film according to this method and, thereby, physical conversions, including conversion from a crystalline state to an amorphous state and recrystallization, are carried out. Accordingly, problems arise when the manufacturing process becomes complicated and, in addition, a high quality substrate in which crystal defects have been sufficiently reduced cannot be realized as the final substrate due to physical conversion into the amorphous state.